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Programming - common sense CS

2022-07-21 15:27:00 【Come on, jump】

\u0001

Hexadecimal escape sequence ： Such as \x1abf4 , Any number of hexadecimal digits can be used , Until it is not a hexadecimal digit ;
16 Bit universal character name （universe-character name）：\u It has to be followed by 4 Hexadecimal numbers （ If there are less than four digits, fill them with zeros ）, Express Unicode In the 0 to 0xFFFF Code points within （ But it doesn't mean 0xD800 To 0xDFFF Code points within ,Unicode Within the specified code range , Does not represent the character ）;
32 Bit universal character name ：\U It has to be followed by 8 Hexadecimal numbers （ If there are less than eight digits, fill them with zeros ）, Express Unicode All possible code points in （ except 0xD800 To 0xDFFF outside ）

Java The character type in takes two bytes , Because it supports Unicode Character set . stay C The language used is ASCII Character set , So its character type only takes one byte .Unicode The character set is used to support all languages in the world ,ASCII The character set is just a subset of it , To be exact , It is Unicode The first part of the character set 255 Characters . therefore , all ASCII All characters in the character set are Unicode Legal characters in the character set .Unicode The characters of a character set are often represented in hexadecimal , for example ‘\u0000’、‘\u0028’、‘\uffff’ etc. . It ranges from ‘\u0000’ To ‘\uffff’, among ‘\u0000’ To ‘\u00ff’ yes ASCII Characters in the character set .‘\u’ It is also an escape character , Used to indicate that the next four hexadecimal digits are Unicode Character code .

-D

usage ： -DpropertyName=propertyValue

effect ： Configure the target parameters of the plug-in

example , For example, we often use maven Execute the local installation command install Skipping unit tests is mvn install -Dmaven.test.skip=true.

Parameters -D yes Java Self contained , Its function is to set Java System properties of ,Maven Just reuse this parameter . Then you can check the system properties when preparing the plug-in , Then the global configuration of plug-in parameters is realized .

UUID

msg	analysis	remarks
36 position
Remove the center line 32
Distribution 8–4–4–4–12

springboot Priority of configuration file

priority
Command line mode > Configuration file mode

The order in which the configuration file is read is ：properties->yaml->yml;

bootstrap and applicaton
bootstrap Load takes precedence over applicaton.bootstrap Mainly used to load configuration information from additional resources , You can also decrypt properties in the local external configuration file .

java The secret of startup

java [options] -jar xxx.jar [arguments]

msg	analysis	remarks
among [options] Express Java Optional configuration information of the running environment , It will affect java Running environment , Is the key to performance tuning , And you can pass multiple options .
[arguments] It represents the parameters of the program itself , It will be sent to main In the parameter array of the function , Used by the program itself .

first options There are three categories

many？ Space off

msg	analysis	remarks
Standard Options	-D	-Dfile.encoding=UTF-8 -Dspring.profiles.active=dev
Nonstandard Options	-X For the identity , be used for java tuning	-Xms1024mJava The initialization size of the heap is set to 1G
Unstable Options	Unstable options are also nonstandard , It is equivalent to a subset of non-standard options , Are subject to -XX start	XX:+UseG1GC Use G1 Garbage collector .XX:+PrintGCDetailsGC Enter the details of garbage collection in the log XX:OnOutOfMemoryErrorOOM Time output dump file .